This can be quite interesting for game development on the Atari ST/STE. Please find attached an archive containing MAME GLSL shaders which are able to remap the arcade games colours to a given 16 colours palette of the Atari ST/STE.

PrerequisitesMAME and some arcade ROMs to check out the remapping.

InstallationCopy the folder GlslRemap of the attached archive to the MAME folder.

This example starts the MAME arcade game "Ghouls'n'Ghosts" using the shader to remap the game colours to a special Atari ST palette of 16 colours including some mixed (checkered) colors. So in fact the total number of remapped "virtual" colours in this case is 38.

You can create and use your own palette using this online tool by uploading an image containing all colours of your palette and copy and paste the created shader snippet into the given code. This is a bit awkward but probably you may find it useful for your needs.

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I hope I'll find a way to capture OpenGL screens from MAME. So far I only get black images at least from my MacBook. Probably I should make a HD video to show the results for those who wonder how it looks like.